Sydney Monthly Climate Summary: July 2006
Wet and cloudy July for coastal Sydney

Tuesday 1 August, 2006

In Brief

Wettest July since 1999, total of 140.2 mm.
However, below average rainfall in far western suburbs.

15 rain days, last exceeded in July
1950 (when 21 days).

Above average temperatures.

Cloudy month with below average sunshine,
only 5.9 hours/day (lowest for 5 years).

Coastal Sydney recorded 3 fogs, highest
for July since 1950 (when 4 fogs).

Details

Rainfall:

Sydney's total rainfall of 140.2 mm was well
above the historic average1 of 97.5 mm and the wettest July since
1999 (when 182 mm was recorded). There were 15
rain days during the month which was last equalled in 1984 and last
exceeded in July 1950 (when 21 rain days). The historic average
is 10 rain days. Much of the rain fell during the second half of
the month with heavy showers and rain periods associated with a
low-pressure trough over NSW and a moist SE air
stream. However, the heavy rain was confined mainly to south-eastern
coastal suburbs with much lighter falls extending to
far western and northern suburbs where below average rainfall
was recorded. Metropolitan rainfall for July ranged from 233.8 mm at
Rose Bay in Sydney's east (the 3rd wettest July in 40 years of record)
to only 18 mm at St Clair in Sydney's far west.

The wet July follows above average rainfall in June with
a 2-month total of 317 mm, the highest for consecutive months at
Observatory Hill since April-May 2003 (when 541 mm).

Warragamba catchment: July rainfall totals
over the catchment area were generally 40−60 mm, with isolated heavier
totals of 80−100 mm at fringe locations of Katoomba and Bowral.
Recent rainfall over Sydney's catchments can be found on
the Sydney Catchment Authority web site
http://www.sca.nsw.gov.au/dams/rainfall.html.

Temperatures:

Above average temperatures were recorded in Sydney
during July, making it the 8th consecutive July with above average
temperatures. The average monthly mean temperature (the average of the daily maximum
and minimum temperatures) of 13.5°C was above the historic
average1 of 12.8°C and ranks as the 10th highest since
records commenced in 1859. Days were cool to mild with the average maximum
day-time temperature of 17.9°C at Observatory Hill being
above the historic average of 17.1°C. The average maximum temperature
at the more elevated locations of Terrey Hills and Springwood was about
2°C cooler.

Nights were cool to mild with the average minimum temperature at
Observatory Hill being 9.1°C, which was also above the historic
average of 8.4°C. However, nights were progressively cooler in
suburbs further from the coast and particularly
cold in the western suburbs during the first 2 weeks of July when
Richmond's temperature fell to −3.3°C on the 9th, the lowest Metropolitan
temperature for the month.

The highest temperature at Sydney (Observatory Hill)
during July was 23.0°C on the 11th while the lowest was 5.8°C on the
9th. Corresponding extremes across the Sydney metropolitan area ranged
from 23.7°C at Sydney Airport on the 11th to −3.3°C at Richmond on
the 9th.

Other phenomena:

Generally cloudy conditions prevailedduring the month with an average of 5.9 hours of sunshine
per day, the cloudiest July since 2001 (when 5.0 hrs/day).
Because of the rain and high humidity, there were more fogs than
usual over the Metro area. Fog occurred in coastal locations on
the 15th, 16th and 27th with widespread mist on the 23rd. This is the
highest number of fogs in July since 1950 (when 4 fogs). The historic
average for July is 1 fog.
Visibility was reduced to 600 metres on the 16th, closing the airport
for several hours, while during the early hours of the 27th visibility
fell to 200 metres in the city area. Fog and low cloud was
also frequent over higher parts of the Blue Mountains with Katoomba
recording 11 fogs during July (historic average 3 fogs).
Lightning and distant thunder was reported on 4 days but no thunderstorms
were recorded at the official site at Observatory Hill.

Climate summary for Sydney, July 2006

Sydney Observatory Hill (Elev
39 m)

July 2006

Historic average

July 2005

Average maximumtemperature (°C)

17.9

17.1

19.0

Average minimumtemperature (°C)

9.1

8.4

9.3

Meantemperature (°C)

13.5

12.8

14.1

Monthly rainfall(mm)

140.2

97.5#

62.8

Number ofrain days

15

10

7

Average dailysunshine (hours)

5.9

6.6

7.7

Average relative humidity at 3pm (%)

56

52

49

Number of thunderstorms

0

1

0

Number of windy days*

3

4

2

# median July rainfall is 75 mm..

*windy
day defined as average wind speed of 40km/h or greater at synoptic times.

* recorded at Sydney
Airport # new station, extremes not yet available

This statement has been prepared based on information available at noon on 01/08/06. Although every effort has been made to check them, it is possible that results may change as new information becomes available.

A note about deciles: Deciles are used to give an element (in this case rainfall or temperature) a ranking. Deciles are calculated by arranging the totals in ascending order (from lowest to highest) then splitting them into 10 equal groups (thus the groups are called deciles). The first group would be in decile range one, the second group in decile range two, etc up to the highest annual totals (highest 10 per cent) being in decile range 10.

1Averages: Historic average temperatures for Observatory
Hill and Richmond are based on the period 1961 to 1990 which is a convention of the World Meteorological Organisation.
Average temperatures for Parramatta are based on all available data, 1968 - 2005 and Camden
1972 - 2005. Rainfall averages and extremes for Observatory
Hill are based on all
years of record 1859 - 2005.

The latest rainfall and temperature maps are available here
Climate averages for New South Wales localities are available here
Daily Weather Observations for selected New South Wales localities are available here